Fluidic switching circuit

ABSTRACT

The invention relates to a fluidic pressure-ratio switching circuit, which gives an output signal only when one of a pair of input signals is higher than another. A fluidic bistable device performs the switching function and a fluidic proportional amplifier provides the output signal, the outputs of the bistable device being used to provide control signals for the proportional amplifier. The output of the bistable device which causes the proportional amplifier to give the circuit output signal is connected to the appropriate control port of the amplifier via a further fluidic device which is monostable. The further device may either be inherently monostable or be a biased bistable device. It will in either case provide the appropriate control signal to the amplifier only when the corresponding output signal from the first bistable is present. The power inputs to all the devices are provided from a common source, those of the first bistable and the further device via flow restrictors.

United. States Patent [72] Inventor Ronald Alfred Heath Birmingham, England [21] Appl. No. 858,771 [22] Filed Sept. 17, I969 [45] Patented Sept. 7, 1971 [73] Assignee Joseph Lucas (Industries) Limited Birmingham, England [32] Priority Sept. 30, I968 [33] Great Britain [31] 46265/68 [54] FLUIDIC SWITCHING CIRCUIT 6 Claims, 2 Drawing Figs.

[52] US. Cl 137/8l.5, 235/201 [51] Int. Cl FlSc 1/12 [50] Field of Search 137/8 I .5; 235/200 PF, 20] PF [56] References Cited UNITED STATES PATENTS 3,339,571 9/1967 Hatch, Jr. 137/8l.5 3,338,515 8/1967 Dexter 137/81.5 3,399,829 9/1968 Richards et a1. 137/815 X Primary Examiner-Samuel Scott Attorney- Holman & Stern ABSTRACT: The invention relates to a fluidic pressure-ratio switching circuit, which gives an output signal only when one of a pair of input signals is higher than another. A fluidic bistable device performs the switching function and a fluidic proportional amplifier provides the output signal, the outputs of the bistable device being used to provide control signals for the proportional amplifier. The output of the bistable device which causes the proportional amplifier to give the circuit output signal is connected to the appropriate control port of the amplifier via a further fluidic device which is monostable. The further device may either be inherently monostable or be a biased bistable device. It will in either case provide the appropriate control signal to the amplifier only when the corresponding output signal from the first bistable is present. The power inputs to all the devices are provided from a common source, those of the first bistable and the further device via flow restrictors.

' device") has an inlet port, a pair of outlet ports and a pair of control ports. The device operates on the known wall attachment effect and is such that the supply of pressure to either control port prevents wall attachment in the region of that port to cause flow from one outlet port at a proportion of l the inlet pressure. The device is bistable in that once flow from either outlet port has been established such flow will continue until pressure is applied to the other control port to switch over the flow. The device also has a dump port through which the outlet port which, at any time is not receiving the through flow is vented.

The other type of device used is referred to hereinafter as a proportional amplifier device" and comprises an inlet port through which fluid enters the device and emerges through a nozzle into a vented chamber from which two outlet ports diverge. Two control ports open into opposite sides of the vented chamber and the device is such that the pressures at the two outlet ports are continuously variable with the pressures at the two inlet ports. The ratio of the outlet port pressures is a direct function (preferably a linear function) of the ratio of the control port pressures.

A fluidic switching circuit in accordance with the invention comprises a bistable fluidic device with its inlet port connected through a first flow restrictor to a supply pressure source, and its control ports connected to a pair of independent signal pressure sources, a fluidic proportional amplifier device with its inlet port connected to said supply pressure source and one of its control ports connected to one of the outlet ports of the bistable fluidic device and a further fluidic device having an inlet port connected through a further flow restrictor to the supply pressure source, a control port connected to the other outlet port of the bistable fluidic device and an outlet port, from which there is a pressure output only when there is a pressure signal at said control port, connected to the other control port of the fluidic proportional amplifier device.

The further fluidic device may be a bistable device in which a constant bias pressure is applied to one of the control ports, thereby rendering the device monostable. Alternatively it may be a known monostable device in whichthe inlet port is asymmetrically arranged relative to the outlet ports so that flow from one outlet port is stable and flow from the other outlet port only occurs during the application of a signal pressure to the control port.

Examples of the invention are shown diagrammatically in FIGS. 1 and 2 of the accompanying drawings.

The circuit shown in FIG. 1 includes a bistable device with an inlet port 11, a pair of outlet ports l2, l3 and a pair of control ports 14, 15. When the pressure at port 14 exceeds that at port 15 there is flow from port 12 and when the pressure relationships at ports l4, 15 are reversed there is flow from ports 13. Inlet port 11 is connected via a flow restrictor 16 to a supply pressure source P. Ports l4, 15 are connected to two signal pressure sources P and P which are independently variable.

The circuit also includes a fluidic proportional amplifier device 17 with its inlet port 18 connected to the source P. The device 17 has outlet ports 19, 20. The output of the circuit is taken from port 19 and port 20 is open to atmosphere. The vented chamber 21 of the device 17 is likewise open to atmosphere. The device has control ports 22, 23 such that rising pressure at one of these ports causes a rise in pressure at ports 20, 19 respectively. The port 22 is connected directly to port 13 of the bistable device 10.

A monostable fluidic device 24 controls the pressure at port 23. This device is of the known asymmetrical wall attachment effect type and has an inlet 25 connected via a flow restrictor 26 to the source P. The outlet port 27 through which fluid normally discharges from the device is vented to atmosphere. The

control port 28 is connected to the port 12 of the device 10 and the outlet port 29 from which fluid discharges only when there is a signal at port 28 is connected to the port 23 of device 17.

In use, when the pressure P is'lower than P,the device 10' will deliver its output from port 13, port 12 being substantially atmospheric pressure. There is thus no output fromport 29 of 0 the device 24 and device 17 will thus be delivering all its output via port 20. Port 19 will be at substantially atmospheric pressure. When p rises above P device 10 will switch over thereby bringing port 13 down to atmospheric pressure. Device 24 delivers its output from port 29 at a pressure determined by the restrictor 26 (and the losses in the device 24 itself). This controlled pressure is applied to port 23 of device 17, while port 22 is at substantially atmospheric pressure. The output of device 17 is therefore delivered from port 19. The restrictor 26 is adjusted so that the ratio of the pressures P and at port 23 give maximum pressure recovery at port 19. The

pressure P at port 19 will not vary with the signal pressures P and P except when three is a change in these which operates the bistable device 10.

FIG. 2 shows an alternative form of circuit in which the further fluidic device is a bistable device 30, having control ports 31, 32, inlet 33 and outlets 34, 35. Control port 32 is supplied with a bias pressure derived from the supply pressure P through a flow restrictor 36. The output of the device 30 will thus remain at the outlet 34 unless a pressure signal is applied to the control port 31.

The circuit provides a fast switching characteristic and there is substantially no hysteresis.

It is to be noted that the ambient pressure around each fluidic device in each case may be maintained at a level other than the existing atmospheric pressure. This can result in better switching of the bistable devices with the result that higher pressures are passed from the outlet ports to the control ports of the devices in the following stage or stages.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

l. A fluidic switching circuit comprising a bistable fluidic device with its inlet port connected through a first flow restrictor to a supply pressure source, and its control ports connected to a pair of independent signal pressure sources, a fluidic proportional amplifier device with its inlet port connected to said supply pressure source and one of its control ports connected to one of the outlet ports of the bistable fluidic device and a further fluidic device having an inlet port connected through a further flow restrictor to the supply pressure source, a control port connected to the other outlet port of the bistable fluidic device and an outlet port, from which there is a pressure output only when there is a pressure signal at said control port, connected to the other control port of the fluidic proportional amplifier device.

2. A circuit as claimed in claim 1 in which an outlet port of the said further device, through which fluid normally discharges is connected to atmosphere.

3. A circuit as claimed in claim 1 in which one of the outlets of the proportional amplifier device is connected to atmosphere and a pressure signal forming the circuit output is derived from the other of the outlets.

4. A circuit as claimed in claim 1 in which the said further device is a bistable device including a biasing means so that, in the absence of a pressure signal at the said other outlet of the first-mentioned bistable, there is no output to the amplifier device.

5. A circuit as claimed in claim 1 in which the said further device is a monostable device.

6. A circuit as claimed in claim 5 in which the said biasing means is a pressure signal derived from the supply pressure and applied to a control port of the said further device. 

1. A fluidic switching circuit comprising a bistable fluidic device with its inlet port connected through a first flow restrictor to a supply pressure source, and its control ports connected to a pair of independent signal pressure sources, a fluidic proportional amplifier device with its inlet port connected to said supply pressure source and one of its control ports connected to one of the outlet ports of the bistable fluidic device and a further fluidic device having an inlet port connected through a further flow restrictor to the supply pressure source, a control port connected to the other outlet port of the bistable fluidic device and an outlet port, from which there is a pressure output only when there is a pressure signal at said control port, connected to the other control port of the fluidic proportional amplifier device.
 2. A circuit as claimed in claim 1 in which an outlet port of the said further device, through which fluid normally discharges is connected to atmosphere.
 3. A circuit as claimed in claim 1 in which one of the outlets of the proportional amplifier device is connected to atmosphere and a pressure signal forming the circuit output is derived from the other of the outlets.
 4. A circuit as claimed in claim 1 in which the said further device is a bistable device including a biasing means so that, in the absence of a pressure signal at the said other outlet of the first-mentioned bistable, there is no output to the amplifier device.
 5. A circuit as claimed in claim 1 in which the said further device is a monostable device.
 6. A circuit as claimed in claim 5 in which the said biasing means is a pressure signal derived from the supply pressure and applied to a control port of the said further device. 